In recent years, in the field of motors, anisotropic rare earth bonded magnets have started to be used, and the motor performance has been significantly improved. However, needs for higher performance and reduction in size have been strong, and further improvement in motor performance has been required.
In the fields of automobiles and the like, motors are used at a high temperature in many cases, and hence heat resistance thereof is required. In addition, when used in an organic solvent such as gasoline, motors are also required to have corrosion resistance in that solvent.
An anisotropic rare earth bonded magnet used for motors for automobiles and the like, which are used in an organic solvent, has been required to simultaneously satisfy high motor properties, heat resistance, and corrosion resistance in an organic solvent.
Heretofore, a magnet which has been used is a sintered ferrite magnet having corrosion resistance. However, because of needs for improvement in motor performance, the use of the anisotropic rare earth bonded magnet has been studied.
As a conventional anisotropic rare earth bonded magnet which is used at room temperature and in the atmosphere, a magnet is used which is formed by compounding an anisotropic rare earth powder and a bisphenol-A type epoxy resin, followed by molding. Subsequently, this anisotropic rare earth bonded magnet is entirely coated for corrosion resistance and is adhered to a motor housing for the use.
Hence, since the coating and the adhesion layer are present between the motor housing and the anisotropic rare earth bonded magnet, which form a magnetic circuit, an air gap on the magnetic circuit is generated, and as a result, as motor properties using this magnet, the potential ability of the anisotropic rare earth bonded magnet could not be sufficiently extracted.
Furthermore, since a bisphenol-A type epoxy resin is inferior in heat resistance, it is difficult to use the above bonded magnet for automobile application that requires heat resistance.
In addition, a common bisphenol-A type epoxy resin is coated with an epoxy resin which is the same type as the above resin; however, in this case, the corrosion resistance in an organic solvent is inferior.